A Rare Case of Synchronous Oncocytoma and Angiomyolipoma of the Kidney

BACKGROUND The co-occurrence of renal oncocytoma and angiomyolipoma is exceedingly rare. To date, 17 such cases have been reported in the literature. This report describes a unique case of that association that presented as a single renal mass on imaging. CASE REPORT A 75-year-old woman presented with epigastric discomfort. A CT scan of the abdomen revealed a 6.6×5.7×4.7 cm enhancing right renal mass. Gross examination revealed a nodular, well-circumscribed, tan-brown mass located in the lower pole of the kidney that was abutting the renal capsule. Interestingly, superior to this mass, there was an adjacent, pale tan-white, firm, well-circumscribed nodule in the mid-pole, which was not detected on the CT scan and grossly extended to 1.1 cm of the overlying renal capsule. Histologically, the larger tumor showed characteristic features of oncocytoma. The smaller tumor had an admixture of mature adipose tissue, smooth muscle, and vessels, consistent with a renal angiomyolipoma. CONCLUSIONS We present a new case of synchronous renal angiomyolipoma and oncocytoma, which were uniquely adjacent and coexisted with minimal intermingling renal parenchyma. Other "eosinophilic renal tumors" are significant differential diagnosis considerations. Due to the close proximity of these lesions, this association can present clinically and radiologically as a single renal mass. Careful examination of the nephrectomy specimen is essential for the proper detection of small-sized tumors.